This invention relates to a differential power transmission often referred to as a planetary transmission of the type where the planetary gears radially outward movement is restrained by a planet carrier rather than a ring gear formed within the transmission housing. In general, such transmissions comprise rotatable shafts mounted in axial alignment with one being power driven and the other an output shaft. It also includes planetary shafts radially spaced from the input shaft and driven by a carrier attached to the input power shaft. Gears or pinions are mounted on the planetary shafts and positioned to mesh with a stationary sun gear and a gear mounted on the output shaft. Such transmissions are capable of producing speed differentials of up to 300 to 1.
Because of high output loads and high rotational speeds of the planet carrier assembly in planetary transmissions of the type described above, gears must be very carefully designed, manufactured and assembled. It is essential that the planet gears be accurately positioned at all times to equally distribute the internal tooth loads. Normal design practice would require the planet carrier rotate around a fixed center on the centerline of the output shaft. This invention proposes that the carrier find its own rotational center by being supported by its planet gears as they roll around their respective sun and output gears, the planet gears under load will seek their own operating centers and thus insure equal tooth loading. Whether the planet carrier employs two or three sets of planets the carrier will always retain in its proper spacing due to the planet gears in mesh with their associated sun and output gears. To allow the planet assembly freedom to find its own rolling center, it must not be restrained by torque transmission from the input shaft supported by its own bearings. The input torque must be transmitted through a flexible coupling. However in designs that integrate the driving means with the transmission means, the flexible coupling may be eliminated by using the planet carrier assembly as one of the drive shaft supporting bearings. The pinions gears rolling around the stationary and output gears would be the equivalent of balls in a ball bearing.
Attempts have been made in the prior art to make some of the gears in a planetary transmission float to enable them to more accurately align with intermeshing gears. Such attempts include the use of floating sun gears that move radially relative to the planet gears and cradles in the outer surface of the carrier which drive the planet shaft but enable the shafts to move radially relative to the carrier and the stationary and output gears. However, most of these attempts were associated with transmissions using ring gears. Although both of these methods allow some radial movement between the planet gears and the stationary and output gears, neither has satisfactorily solved the alignment and load distribution problems between the intermeshing gears especially those that do not use ring gears to retain the planet gears.
This invention overcomes the problems in the prior art by providing a means whereby the planet carrier can move in a radial direction thus enabling the planet gears to self align themselves with the gear they engage. This results in a more accurate alignment between the gears which enables the planetary gears to equally share the load being transmitted. This invention will reduce the cost of manufacturing planetary transmissions of the type described by broadening manufacturing gear tolerances, angular pinion gear spacing tolerance, as well as the center distances between the planet pinions and their mating gears.